A study is in progress for the purpose of examining the effects of reduced blood and oxygen supply on the function and metabolism of the mammalian heat. Investigations make use of diving seals. Recent studies in this and other laboratories have shown that the adaptations of seals and other marine mammals to diving asphyxia are specific and highly developed examples of general vertebrate adaptations to asphyxia. Specific research projects are: Studies of adaptations of seal heart to asphyxial hypoxia of diving, including: myocardial metabolism, determinants of oxygen consumption, development of collateral circulation in response to ischemia and mitochondrial function hypoxic and ischemic myocardium. The methods include the use of radioactive-labeled microspheres for determination of myocardial blood flow distribution, catheter-tip pressure transducers for measurement of ventricular pressures, implanted ultrasonic microcrystals for measurement of mycardial dimension changes and wall thickness, catheterization of arteries and the coronary sinus for obtaining arterio-venous differences of metabolic substrates in the myocardium and mitochondrial extracts prepared from fresh tissues. Recent results indicate that cardiac work is much reduced during diving and intermittent coronary vasospasm occurs.